Recent developments in molecular biology and biochemistry have allowed the use of numerous biologically active components in processes of synthesis, of separation and/or of diagnosis. Among these biologically active components, enzymes proved to be good catalysts due to their strong affinity for their substates and their vigorous catalyst activity functioning under mild conditions.
However, these processes often require a modification of temperature, pH, concentration of reagents, dessication of support, that are frequently at the cause of the denaturation or destruction of the enzymes used. Enzymes are characterized by a specific tridimensional conformation obtained through the arrangement of aminoacids and the bonds existing between these elements. Denaturation reactions induce minor or major modifications of this conformation without necessarily perturbing the aminoacid sequence of the denatured enzymes. This denaturation may result in a decrease or even the complete inactivation of the biological activity of the enzyme.
The acetylcholinesterase enzyme and the menbrane-bound receptor of acetylcholinesterase belong to the enzymes and enzymatic receptors whose spontaneous inactivation at room temperature is very fast. Yet, these two entities possess a great analytical and diagnosis potential for the detection of some kinds of pesticides, the evaluation of the blood level of certain drugs and the diagnostic of some diseases (muscular myastheny, Alzheimer disease, . . .).
Most currently used pesticides possess an inhibitory activity acting on a defined reaction site. Some pesticides, belonging to the group of the carbamates and of the organophosphors, inhibit cholinesterase, with the result that the transmission of the nervous influx is perturbated. The detection of pesticides traces contaminating food either for animal or for human consumption (wine, cereals, fruit juices, baby foods, salads etc . . .) is presently based on a technique of gaseous chromatography. This technique is highly sophisticated and performs well but is also difficult to apply, lengthy and costly. In addition, it does not allow a global i.e. broad determination of the pesticides potentially involved but analyzes the samples submitted for analysis directly in a detailed way for individual pesticides. A diagnostic tool sensitive enough and simple enough to be routinely applied for the detection in the environment of the group of pesticides perturbating nervous influxes by inhibiting cholinesterase is not yet available. The lack of stability of cholinesterase and of its receptor have led to detection kits designed to analyse the activity of the free enzyme (Sigma chemicals). The potential presence of inhibitory substances is inferred from the activity measured. Another approach to monitor the presence of pesticides involves antibodies against some classes of pesticides, which are applied in an enzyme-based immunological determination of these pesticides (Milllipore). These methods are not sensitive enough for the detection of drugs in the serum of treated patients: a diagnostic kit useful for the monitoring of drug levels in the serum of patients treated for myasthenis or Alzheimer disease is now in great demand but has not yet been developed.